Dust shield and pressure element for speaker magnet assembly



c. B. DIGRE 3,492,443

DUST SHIELD AND PRESSURE ELEMENT FOR SPEAKER MAGNET ASSEMBLY Jan. 27,1970 Filed April 14, 1967 INVEN TOR.

CLIFFORD B. D/GRE ATTORNEYS FIG. 4

Z3 Z2 /6 m FI .6 E69 F [6 10 US. Cl. 179-119 4 Claims ABSTRACT OF THEDISCLOSURE A dust seal and pressure element for the magnet assembly of apermanent magnet equipped loudspeaker, the magnet assembly including amagnet frame or pot, a permanent magnet secured within said pot, and apole piece secured to the permanent magnet within the pot.

BACKGROUND OF THE INVENTION In magnet assemblies of most permanentmagnet speakers, the magnet is of generally cylindrical form and adheredat one end to the inner surface of a pair of spaced walls of the magnetframe or pot, the opposite wall of the pot having an openingtherethrough, axially aligned with the magnet. A generally cylindricalpole piece has an outer end disposed concentrically within said openingand a circumferential flange at its inner end, the inner end beingadhered to the adjacent end of the magnet. A generally cup-shaped hollowdust seal element encompasses the pole piece, and at its smallerdiameter end has sealing engagement with an annular shoulder defined bythe flange of the pole piece, the marginal edge of the seal elementengaging the inner surface of said opposite wall of the pot radiallyoutwardly of the opening therethrough, whereby to exclude dust or otherforeign matter from the annular space between the pole piece and theopening in the pot wall.

Heretofore, dust seals on shields have been generally stamped and formedfrom thin sheet material, such as brass, paper and the like, havingrelatively low resilience. The use of a metal dust shield or sealnecessitates the maintenance of extremely close dimensional tolerancesin the space between the opposite walls of the pot, and the axialdimensions of the magnet, pole piece flange and the seal, if effectivesealing is to be achieved. It is well known that, in the mass productionof parts, the costs thereof rise as the dimensional tolerances arenarrowed. Further, in the production and handling of the metal seals,nicks and burrs often occur in the sealing portions thereof, and oftensmall pieces or slivers of foreign matter adhere thereto, largelydestroying the sealing qualities thereof.

In the assembly of the above-described speaker magnet assemblies, themagnets are secured to the pot and to the pole piece by suitableadhesive which is puddled around the opposite end portions of theperipheral surface of the magnet, and on the adjacent portions of thepole piece flange and the magnet engaged wall surface of the pot. Inmany instances, it has been found that, due to rough handling orvibration, the adhesive fails to hold the parts together, and thespeaker is rendered inoperable. Efforts have been made to apply adhesiveto the opposite end faces of the magnet whereby a much improved bond isformed therebetween and the pole piece and pot, and to axially contractor compress the metal seal sufficiently to permit proper inter-positionof the magnet between the pole piece and pot wall without rubbing orscraping the adhesive from the end surfaces of the magnet, to the endthat, release of the sealing element will permit the same to axiallyexpand and press the magnet between the pole piece and the pot wall toachieve an effective bond.

United States Patent 3,492,443 Patented Jan. 27, 1970 Withoutmaintaining costly tolerances, as set forth above, either the seal isaxially contracted or compressed beyond its elastic limit, when theaxial dimensions of the magnet is unduly long, so that it will notexpand sufficiently to apply proper sealing pressure to the pole pieceand pot, or a given magnet will be too short to properly fill the gapbetween the pole piece and the opposite wall surface. In such event, amagnet of proper axial length must be selected from a supply thereof,resulting in loss of assembly time.

SUMMARY OF THE INVENTION The primary object of this invention is theprovision of a combination dust seal and pressure element which can beaxially contracted or compressed to a substantially higher degree thanheretofore without exceeding its limit of elasticity, so that componentparts of a speaker magnet assembly can be prefabricated with greaterdimensional tolerance than heretofore, and be assembled easily and moreeffectively adhered together, and which, when the parts are assembled,will provide a more effective seal. To this end, I provide a hollowcup-shaped member having an axial opening therethrough for reception ofa pole piece, and an outer annular surface portion adjacent said axialopening for sealing engagement with an annular shoulder on the polepiece adjacent its inner end. The marginal edge of the cup-shaped memberis adapted to have sealing engagement with the inner wall surface of themagnet pot radially outwardly of the pole piece receiving opening in thepot wall. The cup-shaped member is made from non-metallic materialhaving a substantially high elastic resiliency or memory, capable ofbeing axially contracted or compressed sufficiently to enable a speakermagnet to be interposed between the pole piece and the opposite wall ofthe magnet pot with generous clearance between the ends of the magnetand said pole piece and pot wall, without exceeding the elastic limit ofthe cup-shaped member. The elastic resiliency or memory of thecup-shaped member is such that, when released from its axiallycontracted state, the member axially expands sufficiently to exert axialsealing pressure against the shoulder and magnet pot and bondingpressure upon the magnet to hold the magnet against movement duringdrying or curing of adhesive applied to the opposite end surfacesthereof and in contact with the pole piece and pot wall surface. Themarginal edge portion of the member in engagement with the adjacent wallof the pot radially expands during axial contraction of the member andradially contracts during axial expansion of the member.

DESCRIPTION OF THE DRAWINGS Referring to the drawings, in which likereference characters indicate like parts:

FIG. 1 is a view in top plan of the magnet pot assembly including thedust seal and pressure element of this invention, and illustrating astep in the method of assembly, some parts being broken away and someparts being shown in section FIG. 6 is a fragmentary section taken onthe line 66 of FIG. 5;

FIGS. 7 and 8 are views corresponding to FIG. showing modified forms ofdust seal and pressure element; and

FIGS. 9 and 10 are fragmentary sections taken on the lines 9-9 and 1010of FIGS. 7 and 8 respectively.

Referring with greater detail to the drawings, a cross sectionallyrectangular magnet frame or pot is indicated generally at 1, the samebeing formed from a bar of iron or steel to provide a tube having spacedparallel side walls 2 and 3 and end walls 4. The side wall 2 is provided with a generally central opening 5 for reception of a cylindricalpole piece 6, the outer end portion of which is disposed within theopening 5, the inner end of the pole piece 6 being formed to provide aradially outwardly projecting circumferential flange 7, which defines anannular shoulder 8. A generally cylindrical permanent magnet 9 isinterposed between the inner end of the pole piece 6 and the side wall 3and is adhered to the pole piece 6 and side wall 3 by layers of adhesive10. The outer end portion of the pole piece 6 is concentric with theopening 5 to provide an annular passage 11 for the usual loudspeakervoice coil, not shown. As is well known, the voice coil moves axially inthe annular passage 11 with very little clearance therebetween and thepole piece 6 and wall of the opening 5. Hence, it is important that dustor other foreign material be excluded from the passage 11, whereby toprevent the same from upsetting the operating characteristics of thespeaker or rendering the same inoperative altogether. Therefore, ahollow generally cup-shaped dust seal 12 is interposed between theshoulder 8 of the pole piece 6 and the inner surface of the side wall 2of the pot. When the above-described pot assembly is used to complete aloudspeaker, foreign matter is prevented from entering the annularpassage -11 from the exterior of the pot 1 by other portions of thespeaker, not shown, but attached to the outer surface of the wall 2.

The dust seal 12 is formed or molded from suitable non-metallic materialhaving substantial elastic resiliency, or memory, such as variouscommercial plastics, glass fibers, or rubber, and is provided at itssmaller diameter inner end with an axial opening 13 for reception of thepole piece 6. As shown, an annular surface portion 14 adjacent theopening 13 sealingly engages the shoulder 8 of the pole piece 6, theouter surface of the member 12 between the annular surface portion 14and the marginal edge 15 thereof being of generally spherical shape. Asshown by broken lines in FIG. 3, the axial dimension or length of thecup-shaped seal or member 12 is greater than the axial dimension thereofin the completed magnet assembly.

In assembling the magnet assembly, the member 12 is placed on the polepiece 6, after which the pole piece is inserted through the opening 5 inthe pot wall 2 with the marginal edge 15 of the seal or cup-shapedmember 12 engaging the inner surface of the wall 2. A centering sleeve16 is then inserted inwardly through the annular passage 11 to properlylocate the pole piece 6 concentric with the opening 5. The pole piece 6and cup-shaped member 12 are then moved in a direction outwardly of theopening 5 to cause the member 12 to be axially contracted or compressedbetween the shoulder 8 and the pot wall 2. This may be accomplished byany suitable means, such as a bifurcated pressure element shown bydotted lines in FIGS. 1, 2 and 4 and indicated at 17. As shown in FIGS.1 and 2, axial contraction of the member 12 results in radial expansionof the marginal edge portion thereof, permitting the member 12 to beaxially contracted a substantial amount from its normal axial length.With the member 12 thus contracted or axially compressed, adhesivematerial .10 is applied to opposite ends of the magnet 9 and the same isplaced within the pot between the pot wall 3 and the inner end of thepole piece 6 in axial alignment with the pole piece 6. Although notshown, it may be assumed that any suitable centering means, such as atemplate or the like, may be used to properly locate the magnet 9. Whenthe magnet 9 is properly placed, the pressure element 17 is removed,permitting the seal or cup-shaped member 12 to axially expand to exertbonding pressure on the flange 7 against the adjacent end of the magnet9 and to press the magnet 9 into bonding pressure with the pot wall 3.The centering sleeve 16 may be then removed and the magnet assembly usedin the building of a loud speaker.

It will be appreciated that, in view of the elastic nature of the member12, which permits the portion thereof adjacent the marginal edge 15 toradially expand, the member 12 may be contracted axially to a fargreater extent than the heretofore used metallic d-ust shields, beforethe elastic limit thereof is reached. Thus, in prefabricating theseveral parts of the magnet assembly, the dimensional tolerances of thepot 1, flange 7, magnet 9 and shield or member 12, in a directionaxially of the pole piece 6 and magnet 9, need not be critical as is thecase when a metallic shield is used.

In present practice, the commercial tolerance in the axial dimension ofmagnets is plus or minus five onethousandths inch, that of the axialdimension of the pole piece flange plus or minus at least oneone-thousandth inch, and that of the inside dimension of the pot framebeing plus or minus five one-thousandths inch. Thus it may be readilyunderstood that, with such a large range of dimensions, the metallicdust shields heretofore used, having a relatively short range of axialexpansion and contraction, have necessitated costly selection ofmagnets, pole pieces and magnet ports, from supplies thereof, to obtainclose fitting magnet assemblies. Further, by molding or otherwisefabricating the member 12 from non-metallic materials, as aboveindicated, the necessity for degreasing and cleaning the seal prior toassembly, is eliminated. Moreover, the elastic resilience of thematerial causes the seal 12 to make effective sealing contact with theshoulder 8 and adjacent inner surface of the pot wall 2, even though thesurface of the pot wall 2 is rough or uneven.

A very definite advantage in the use of the member 12 over a metallicdust seal resides in the fact that it enables the adhesive 10 to beapplied to the entire end faces of the magnet 9, whereby maximum areabonding is achieved between the magnet 9 and pole piece 6 and Wall 3.

If desired by those who have established assembly procedures andapparatus, the layers of adhesive 10 may be omitted, and the magnet 9may be adhered to the magnet pot 3 and pole piece 6 by puddling adhesivearound opposite end portions of the magnet and adjacent surface portionof the pole piece and magnet pot as heretofore done.

As shown in FIG. 1, the bifurcated pressure element 17 engages thegenerally spherical surface of the cup-shaped shield member 12 justradially outwardly of the flange 7. The modified form of cup-shapedmember shown in FIG. 7 and indicated at 18, is formed to provide arelatively larger diameter annular surface portion 19 radiallyou-twardly of the central opening 20 of the member 18, for engagementwith the bifurcated pressure element 17.

The modified form of dust seal shown in FIG. 8, and indicated at 21, isformed to provide a pair of diametrically opposed surface portions 22for engagement of the pressure element 17, radially outwardly of thecentral opening 23 of the member 21.

It will be ap reciated that other suitable means may be employed foraxially contracting the dust seals of this invention, such as a magneticchuck or the like, not shown, applied to the outer end of the pole piece6, if desired.

While I have shown several embodiments of dust seal and pressureelement, it will be understood that the same is capable of furthermodification Without departure from the spirit and scope of theinvention, as defined in the claims.

What is claimed is:

1. A dust seal and pressure element for a speaker magnet assemblyincluding, a magnet pot having spaced side walls and an opening throughone of said side walls, a pole piece extending axially through saidopening and having a flanged inner end defining an annular shoulder inaxially inwardly spaced relation to said opening, and a magnet betweensaid flanged end of the pole piece and the other one of said side walls;said element comprising a hollow generally cup-shaped member having anaxial opening for reception of a pole piece and an outer annular surfaceadjacent said opening for sealing engagement with said annular shoulder,said member having a marginal edge for sealing engagement with said oneof the walls of said pot radially outwardly of said opening, saidcupshaped member being of non-metallic elastic resilient material andhaving a modulus of elasticity such that the member may be compressedaxially a substantial proportion of its normal axial dimension withoutexceeding the elastic limit of the member, said member, adjacent itsmarginal edge, being radially expansible and contraotable responsive toaxial compression and expansion respectively of said member.

2. The dust seal and pressure element defined in claim 1, in which saidannular surface includes fiat transverse surface portions extendingradially outwardly from said axial opening.

3. The dust seal and pressure element defined in claim 1, in which saidcup-shaped member is fabricated from synthetic plastic material havingelastic memory.

4. The dust seal and pressure element defined in claim 2, in which saidmember is of generally spherical shape between said annular surface andthe marginal edge of the member.

References Cited UNITED STATES PATENTS 2,910,546 10/ 1959 Swanson179115.5 3,092,694 6/1963 Walczak 179115.5 3,176,086 3/1965 Coen 1791193,222,753 12/1965 Heppner 179-117 X RALPH D. BLAKESLEE, Primary ExaminerUS. Cl. X.R. 179115.5

